Gas adsorption beds are used in many industries to remove airborne contaminants, such as organic bases, to protect people, the environment and often, a critical manufacturing process or the products that are manufactured. A specific example of an application for gas adsorption beds is the semiconductor industry where products are manufactured in an ultra-clean environment, commonly known in the industry as a “clean room”. The manufacturing processes typically require the use of substances such as solvents to be used in the clean room environment. The use of these substances presents a problem because vapors that are present or are a byproduct from the process may contaminate the air and other processes in the room, such as lithography processes using chemically amplified photoresists, if not properly removed. In addition, environments may have gases that are naturally occurring in the ambient air, contaminants that cannot be removed by particulate filters. Typical previously recognized airborne contaminants include bases, such as ammonia, organic amines, and N-methyl-2-pyrrolidone.
To eliminate the airborne basic contaminants, contaminated air is often drawn through a granular adsorption bed assembly having a frame and an adsorption medium, such as activated carbon, retained within the frame. The adsorption medium adsorbs or chemically reacts with the gaseous contaminants from the airflow and allows clean air to be returned to the process and/or the clean room. The removal efficiency is critical in order to protect the processes and the products. The removal efficiency and capacity of the gaseous adsorption bed is dependent upon a number of factors, such as the air velocity through the adsorption bed, the depth of the bed, the type and amount of the adsorption medium being used and the activity level and rate of the adsorption medium. It is also important that for efficiency to be increased or maximized, the air leaking through voids between the tightly packed adsorption bed granules and the frame should be eliminated. Examples of granular adsorption beds include those taught is U.S. Pat. No. 5,290,245 (Osendorf et al.), U.S. Pat. No. 5,964,927 (Graham et al.) and U.S. Pat. No. 6,113,674 (Graham et al.).
Although the above identified adsorption beds, and other known beds, are used to remove bases, other airborne contaminants are also often present in the contaminated air. What is needed is an adsorption bed that can effectively remove both bases and other contaminants such as acids and other organic materials.